In the PowerShell ISE, there are two key shortcuts that can help you. Pressing TAB works just like in the console, and each time you press TAB, you get a tabexpansion result.
CTRL+SPACE is the other important keyboard shortcut. It opens the IntelliSense menus. Since ISE opens these menus automatically most of the time, most users never took notice of CTRL+SPACE, but it can be useful to re-open a dismissed IntelliSense menu.
And beginning with PowerShell 5.0, CTRL+SPACE becomes even more important, especially when you write DSC (Desired State Configuration) configuration scripts. The PowerShell ISE provides extensive IntelliSense help for DSC but will not open the IntelliSense menus automatically in many cases. Only when you press CTRL+SPACE manually will you get the clever IntelliSense help.
